The present invention relates to cylinders or cylinder liners, hereinafter referred to merely as "liners" when applicable, in an internal combustion engine. More particularly, the invention relates to liners intended for use in diesel engines or compression-ignition type internal combustion engines which operate under severe working conditions for long periods of time.
It is a present day goal to increase the service life of a diesel engine to 700,000 to 1,000,000 km. However, in order to achieve this objective, it is first necessary to solve a problem relating to combustion gas blowing through between the liner and the piston ring of the engine after the engine has been used for more than a half of its service life. That is, the engine suffers from the effects of "blow-by". This phenomenon occurs because the surface of the liner has become so smooth as to be essentially a mirror surface or both of the piston ring and the liner have become considerably worn after the engine has been operated for more than about a half of its service life.
Accordingly, an object of the invention is to provide a liner for an internal combustion engine with which the amount of wear of the liner and a piston ring used therewith are considerably reduced, thereby to positively prevent the occurrence of blow by.
In general, in a cylinder of an internal combustion engine, a region close to the top dead center of the piston is worn out first because not only the combustion gas pressure and the temperature are highest there but also the lubricating conditions are most severe. Accordingly, the phenomena of scuffing and blow-by are liable to occur at the region of the cylinder.
Heretofore, in order to eliminate the above-described difficulties, a liner has been used of which the wear-resistance has been increased by covering with a sprayed layer, plating or hardening to prevent wear of the aforementioned region of the cylinder. The application of such a liner is advantageous in that wear-resistance is improved. However, it is still disadvantageous in that the occurrence of blow-by still is not sufficiently prevented after the engine has been operated for a long period of time. That is, in the case where the region close to the top dead center is completely and uniformly treated to increase it wear-resistivity, a frictional wear differential or wear step is formed between the surface of this region and the adjoining regions. This may result in the occurrence of blow-by. Even with a liner which is hardened in the form of a spiral or spots with a laser beam or the like, the formation of a frictional step cannot be avoided and, accordingly, it is still not possible to prevent blow-by.